The Relationship between Airway Responsiveness Measured before and after the Allergen-Induced Late Asthmatic Response

Single blind allergen (Ag) and saline solution bronchial challenges were performed on two successive study days in ten asthmatic subjects. Histamine challenges were performed before, at approximately 2 h (or after resolution of the immediate bronchial response [IR]), and 24 h after saline solution or Ag inhalation. Specific airway conductance (SGaw) was measured after delivery of challenge agents until a 50 percent fall in SGaw was observed. The SGaw was monitored over 8 h for immediate and late asthmatic responses (LAR). Results were expressed as provocative concentrations eliciting a 50 percent decrease in SGaw (SGawPC50HIS). No significant changes from baseline SGaw or SGawPC50HIS were demonstrated after saline solution. Eight subjects (dual reactors) exhibited both an IR and LAR after Ag and two had isolated IRs. Of the eight dual reactors, five had greater than 50 percent decreases in SGawPC50HIS immediately after resolution of the IR and six exhibited such decrements 24 h after Ag provocation. Mean baseline SGawPC50HIS (N = 10) on the Ag challenge day was 3.2 ±4.59 mg/ml and decreased to 0.92 ± 4.56 mg/ml at 102 to 187 minutes after Ag (p = 0.0009) and was significantly decreased from baseline at 1.47 ±3.8 mg/ml 24 h after Ag (p=0.0004). One of the two patients with isolated IR also showed an early onset increase in airway responsiveness (EOR). There was a significant correlation between the percentage of fall from baseline in SGaw-PC50HIS immediately after the IR and that at 24 h after Ag (r=0.811, p=0.005). There was no significant correlation between the decrease in SCawPC50HIS after the IR and the magnitude of the LAR. These data suggest that (1) the early events occurring prior to the LAR may determine changes in airway responsiveness observed at 24 h after Ag challenge, and (2) the EAR to histamine is not exclusively associated with the LAR.